NDM-1 Overview

NDM-1 is an abbreviated way to write New Delhi metallo-beta-lactamase, which is the name given to a new (discovered in 2009) enzyme that is able to be produced by several genera of bacteria that render the bacteria resistant to many antibiotics in common use around the world. This enzyme belongs to a group of enzymes (beta-lactamases) that are capable of breaking the chemical bonds of a beta-lactam ring, which composes an important part of many antibiotics such as drugs of the penicillin, cephalosporin, and carbapenem groups. Most of the beta-lactamase enzymes are effective on some or most of the older antibiotics like penicillins and cephalosporins. NDM-1, however, is effective on both the old and newer antibiotics (carbapenems such as imipenem) that contain a beta-lactam ring.

Klebsiella were the first bacteria identified (in 2009) to produce NDM-1 in a patient that traveled from India to England with an infection that did not respond to many antibiotics. The organism was resistant to beta-lactams and, after the organism's genetic and antibiotic resistance mechanisms were studied, NDM-1 and its genetic source were discovered. The genetic source was a plasmid termed "blaNDM-1," and since that discovery, other bacterial genera have been found to have blaNDM-1 integrated into other plasmids or into the bacterial chromosome, thus allowing the bacteria to produce NDM-1.

NDM-1, while effective against almost all antibiotics with beta-lactam rings, is not effective in producing antibiotic resistance against other types of antibiotics such as fluoroquinolones (for example, ciprofloxacin [Cipro] and levofloxacin [Levaquin]) or aminoglycosides (for example, gentamicin [Garamycin] and streptomycin [Streptomycin]). Unfortunately, most of the strains of bacteria that have NDM-1 also have either plasmid or chromosomal resistance against these (and other) antibiotics. The term "superbug" is often used loosely to describe organisms resistant to usually two or more antibiotics
that are usually effective. Because bacteria that contain NDM-1 are often resistant to almost every antibiotic, bacteria with NDM-1 have been termed a superbug; some investigators consider these bacteria to represent the most dangerous superbug of all that have developed so far.

Although newly discovered in 2009 and most likely because of genetic transfer of plasmids or other chromosomal segments, NDM-1 has been found in at least four different genera of gram-negative bacteria (Klebsiella, Escherichia, Enterobacter, and Acinetobacter). In addition, people in India, Pakistan, England, Canada, Sweden, Australia, Japan, and the U.S. have been found to be infected with bacterial strains that produce NDM-1. Researchers speculate that the extremely fast spread of NDM-1 may be due to patients seeking medical care outside of their home country (for example, visitors or travelers from India); others suggest the widespread and uncontrolled use of antibiotics favors the survival of NDM-1-containing bacterial strains. Another possible reason for fast spread is that Escherichia coli (E. coli), part of the normal bacteria found in the human intestine, readily exchanges plasmids; in fact, the first identified patient infected with Klebsiella containing NDM-1 was subsequently found to have an E. coli strain, isolated from the feces, capable of producing NDM-1.